|latest/stable||14||14||19 Mar 2021|
juju deploy yoshikadokawa-magpie
Magpie layer to test networking - ICMP and DNS Read more
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Leadership Layer for Juju Charms
The Leadership layer is for charm-tools and 'charm build', making it easier for layered charms to deal with Juju leadership.
This layer will initialize charms.reactive states, allowing you to write handlers that will be activated by these states. It allows you to completely avoid writing leader-elected and leader-settings-changed hooks. As a simple example, these two handlers are all that is required to make the leader unit generate a password if it is not already set, and have the shared password stored in a file on all units:
import charms.leadership from charmhelpers.core.host import pwgen @when('leadership.is_leader') @when_not('leadership.set.admin_password') def generate_secret(): charms.leadership.leader_set(admin_password=pwgen()) @when('leadership.changed.admin_password') def store_secret(): write_file('/etc/foopass', leader_get('admin_password'))
The following states are set appropriately on startup, before any @hook decorated methods are invoked:
This state is set when the unit is the leader. The unit will remain the leader for the remainder of the hook, but may not be leader in future hooks.
This state is set for each leadership setting (ie. the
leadership.set.foostate will be set if the leader has set the foo leadership setting to any value). It will remain set for the remainder of the hook, unless the unit is the leader and calls
reactive.leadership.leader_set()and resets the value to None.
This state is set for each leadership setting that has changed since the last hook. It will remain set for the remainder of the hook. It will not be set in the next hook, unless the leader has changed the leadership setting yet again.
One or more leadership settings has changed since the last hook. This state will remain set for the remainder of the hook. It will not be set in the next hook, unless the leader has made further changes.
charms.leadership module exposes the
leader_get() methods, which match the methods found in the
should be used instead of the charmhelpers function to ensure that
the reactive state is updated when the leadership settings are. If you
do not do this, then you risk handlers waiting on these states to not
be run on the leader (because when the leader changes settings, it
triggers leader-settings-changed hooks on the follower units but
no hooks on itself).
This layer is maintained on Launchpad by Stuart Bishop (email@example.com).
Code is available using git at git+ssh://git.launchpad.net/layer-leadership.
Bug reports can be made at https://bugs.launchpad.net/layer-leadership.
Queries and comments can be made on the Juju mailing list, Juju IRC channels, or at https://answers.launchpad.net/layer-leadership.